Coupling

ABSTRACT

A coupling comprising a first member defining a socket, a second number such as a tube defining a spigot inserted into an open end of the socket, and a locking device received within an annular gap defined between an inner wall of the socket and an outer wall of the spigot. The locking device comprises circumferentially spaced load-bearing members, each load-bearing member extending within the annular gap from a first end which is relatively close to the open end of the socket and a second end which is relatively remote from the open end of the socket. Each load-bearing member is resiliently biased such that the first end engages the socket and the second end engages the spigot, and each load-bearing member is dimensioned such that it acts substantially as a beam in compression to resist withdrawal of the spigot from the socket.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a coupling and in particular a couplingfor joining together a socket and a spigot inserted into the socket.

2. Description of the Related Art

Coupling devices for joining together a socket and a spigot, such as ina pipe fitting, are well known. Many such couplings incorporate alocking ring retaining mechanism. An example of a coupling deviceincorporating such a form of retaining mechanism is disclosed in U.K.Patent Application No. 2,066,914 A. This describes a releasable couplingdevice comprising a fitting having an opening for receiving the end of atube and a retaining ring located in the opening. The retaining ring hasa plurality of axially extending, inwardly biased fingers adapted toengage an inserted tube to restrain it against axial movement out of thefitting. The device is provided with an unlocking collar which may beused to force the plurality of fingers radially outward, therebydisengaging the fingers from the tube.

U.S. Pat. No. 4,696,497 describes a coupling which can be used toconnect a variety of fittings such as fluid lines and electric cables.The coupling comprises a tubular socket dimensioned to receive the endof a tubular spigot. The spigot has recesses formed near its ends whichserve as detent means. A locking ring is inserted into the socket andcomprises a plurality of radially resilient fingers which extend axiallyinto the aperture of the socket, angled so as to have oblique portionsextending towards the mouth of the socket. The diameter of the spigot isgreater than that of an imaginary circle defined by the ends of theresilient fingers. The spigot is pushed into the socket, deflecting theresilient fingers which snap into the recesses. Axial removal of thespigot from the socket is prevented by the location of the fingerswithin the detente recesses. To remove the spigot it must first berotated within the socket to cam the fingers out of the recesses.

Similar devices are known for retaining a cap on the end of a spigot inthe form of a rod which serves for example as an axle in a childs toy.Such cap devices incorporate a cup-shaped casing defining a socket, therim of which is bent inwards to define an annular slot which opensradially inwards. A spring steel disc is retained in the slot, astar-shaped aperture being cut in the disc so that the edges of theaperture define pointed spring fingers extending radially inwards. Thecasing can be secured on the end of a rod the diameter of which isgreater than the diameter of the circle touched by the tips of thespring fingers, simply by pushing the rod into the aperture. This causesthe spring fingers to deflect and bite into the rod so as to prevent itsremoval.

Each of the above described structures has the disadvantage that anyaxial load on the coupling which tends to pull the spigot out of thecoupling is born by the force exerted by deflection of the springfingers. The greater the load applied to the coupling, the more thespring fingers will bend. By the very nature of springs, a bent springwill store energy. As the load applied to the coupling is increasedthere comes a point when the energy stored in the spring fingers issufficient to cause them to deflect into a shape which disengages themfrom the spigot. The coupling then fails.

SUMMARY OF THE INVENTION

Alternatively the spring fingers may simply yield or snap under highload as their strength is limited by the need to be flexible. The springfingers cannot be made very stiff or they will not be able to engage thespigot under light loads.

It is an object of the present invention to provide a coupling whichobviates or mitigates the above disadvantages.

According to the present invention there is provided a couplingcomprising a first member defining a socket, a second member defining aspigot inserted into an open end of the socket, and a locking devicereceived within an annular gap defined between an inner wall of thesocket and an outer wall of the spigot, wherein the locking devicecomprises a plurality of circumferentially spaced relatively stiff loadbearing members interconnected by relatively flexible interconnectingmeans, each load bearing member extends within the annular gap between afirst end which is relatively close to the open end of the socket and asecond end which is relatively remote from the open end of the socket,and the interconnecting means resiliently bias each load bearing membersuch that the first end engages the socket and the second end engagesthe spigot, the interconnecting means enabling each load bearing memberto pivot about the first and second ends substantially independently ofthe other load bearing members, such that each load bearing member actsas a beam in compression to resist withdrawal of the spigot from thesocket.

The locking device may comprise an annular member of resilient materialdefining a front face, a back face, a radially inner surface and aradially outer surface, the annular member being provided with aplurality of radial slots grouped in pairs, one slot of each pairextending radially outwards from the radially inner surface of theannular member and the other extending radially inwards from theradially outer surface of the annular member, the arrangement being suchthat a load bearing member is defined between neighbouring pairs ofslots and each pair of slots defines the resilient interconnectionbetween adjacent load bearing members.

Preferably the annular member is provided with apertures extendingradially therethrough at the location of each pair of slots.

In an alternative arrangement the locking device may comprise anarrangement of individual load bearing members supported within a collarof elastomeric material. The said collar may then provide both theresilient interconnection between adjacent load bearing members and thesaid biasing means.

It will be appreciated that the annular arrangement of the load bearingmembers need not be circular but could be any required configurationdepending on the profile of the spigot and socket.

In an embodiment of the invention in which either the spigot or thesocket defines a cylindrical surface against which the load bearingmembers bear, the portion of the load bearing members which bear againstthe cylindrical surface may define sections of a helix such that thecoupling may be disengaged by relative rotation between the spigot andsocket. Both the radially inner and outer ends of the load bearingmembers may define helices, each engaging a respective cylindricalsurface, in which case the coupling will disengage whichever surface thelocking member slides relative to as a result of rotation.Alternatively, one of the radially inner and outer edges of the lockingdevice defines a helix and is free to slide relative to the surfaceagainst which it bears, whereas she other edge defines a circle and isprevented by keys or other suitable formations from sliding relative tothe surface against which it bears, or the other edge defines anon-circular shape matching the shape of the surface it engages suchthat relative rotation is not possible.

BRIEF DESCRIPTION OF THE DRAWINGS

A spreader plate may be provided around the spigot to spread the leadapplied by the locking device over the surface of the spigot.Furthermore, a stiff insert may be provided inside the spigot to supportthe spigot against radial loads applied by the locking device. Theinsert preferably defines an annular groove facing radially outwards andaxially aligned in the assembled coupling with the locking device.

Embodiments of the present invention will now be described, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 is a front elevation of a locking device of a coupling accordingto an embodiment of the present invention;

FIG. 2 is a cross-section of FIG. 1 taken on the line A--A;

FIG. 3 is a cross-section of a simple coupling incorporating the lockingdevice of FIGS. 1 and 2;

FIG. 4 illustrates a modification of the locking device of FIGS. 1 and2:

FIG. 5 is a cross-section of a pipe coupling according to the presentinvention;

FIGS. 6 to 8 illustrate three alternative releasable couplings accordingto the present invention;

FIG. 9 illustrates a component of a coupling according to the presentinvention adapted to be used in conjunction with a soft spigot;

FIG. 10 illustrates a first coupling incorporating the component of FIG.9;

FIG. 11 illustrates a second coupling incorporating the component ofFIG. 9;

FIG. 12 is a part section of a coupling according to the presentinvention adapted to support a fitting;

FIG. 13 illustrates the coupling of FIG. 12 incorporating the componentof FIG. 9; and

FIG. 14 illustrates a coupling according to the present inventionadapted for use as an electrical connector:

FIGS. 15 and 16 are views from opposite sides of a locking device inaccordance with the invention received in a six-sided socket;

FIGS. 17 and 18 are sections on lines 17--17 and 18--18 of FIG. 15; and

FIG. 19 illustrates a further embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2 the illustrated locking device comprises ametal ring defining a back face 1, a radially inner surface 2, aradially outer surface 3, and a front face 4. The ring is provided witheight equidistant pairs of slots 5 and 6. Each pair of slots comprises aslot 5 extending radially inwards from the outer surface 3 of the ringto a depth just less than the radial thickness of the ring, and asubstantially parallel slot 6 of the same depth but which extendsradially outwards from the inner surface 2 of the ring. The slots 5 and6 are the same width. The pairs of slots 5 and 6 define strut portions 7and spring portions 8 of the ring. The resultant arrangement is anannular array of struts 7 resiliently interconnected by a series ofsprings 8. The struts 7 are therefore capable of a significant freedomof movement with respect to one another.

In cross-section, as shown in FIG. 2, the radially inner and outersurfaces, 2 and 3, of each strut are parallel and inclined at an angleof approximately 5° to the central axis of the ring. The front and backfaces, 4 and 1, of each strut 7 are also parallel and are inclined at anangle of approximately 15° to a radius drawn to the centre of the ring.Thus the radially outermost circumference 9 of the ring is defined bythe outer radius of the front face 4 and the radially innermostcircumference 10 of the ring is defined by the inner radius of the backface 1.

The basic manner in which the abovedescribed locking device is employedin a simple coupling is illustrated in FIG. 3. The locking ring isinserted into a socket 11 of a fitting 12 which is to receive a spigot13. The dimensions of the ring are chosen such that prior to insertioninto the socket 11 the radially outermost circumference of the ringdefined by the edges 9 has a diameter slightly greater than the internaldiameter of the socket 11. The flexibility of the ring due to the springportions 8 allows the ring to be pushed into the socket 11 to form atight fit therewith with the edges 9 of the struts 7 bearing against theinner surface of the socket 11. The spigot 13, which has a diameterslightly greater than the internal diameter of the ring defined by theedges 10 of the struts 7, is then inserted into the socket 11 throughthe ring. Again, the flexible nature of the ring allows the spigot 13 tobe pushed therethrough forming a tight fit with the edges 10 of thestruts 7 bearing against the surface of the spigot 13.

If an axial force is now applied to the spigot 13 to withdraw it fromthe socket 11, the frictional force between the spigot 13 and the edges10, and the frictional force between the inner wall of the socket 11 andthe edges 9, will cause the edges 9 and 10 to bite into the socket 11and spigot 13 respectively. Once the edges 9 and 10 of the struts 7 havebitten into the socket 11 and spigot 13 they form effective hinges aboutwhich the struts 7 will tend to pivot as further axial load is appliedto the coupling. The length of the struts 7, i.e. the distance betweenthe edges 9 and 10, is greater than the annular separation of the socket11 and spigot 13. Thus the pivotal action of the struts 7 about thehinges formed by the edges 9 and 10 will tend to compress the struts 7,with a resultant force being applied between the socket 11 and thespigot 13 which will retain the spigot 13 within the socket 11.

The load bearing capability of the coupling will be determined by theability of the struts 7 to withstand the compressive force exertedthereon. The greater the axial load on the coupling, the greater will bethe compression of the struts 7 and therefore the greater will be theforce applied by the struts 7 to the spigot 13 and socket 11. Thereforeprovided the struts 7 are constructed from a sufficiently strongmaterial, i.e. preferably at least as strong as the material from whichthe spigot 13 and socket 11 are constructed, and provided they aresufficiently thick, then the coupling will be able to withstandsignificant loads. Tests have shown that couplings of this sort canwithstand loads of up to an order of magnitude greater than the loadsthat can be born by the prior art couplings described above which relyupon spring fingers to resist axial loads.

In one embodiment of a locking ring as illustrated in FIGS. 1 and 2, thering had the following dimensions:

axial width of radially inner surface 2=11 mm

axial width of radially outer surface 3=12 mm

radial width of back face 1=6 mm

radial width of front face 4=5 mm

width of slots 5 and 6=1 mm

separation of slots 5 and 6=1 mm

The load bearing capabilities of this type of coupling are derived fromthe structure of the locking ring and the fact that each of the struts 7acts essentially independently of the others. Thus the spring forceexerted on the struts 7 by the spring portions 8 is negligible comparedwith the compressive forces exerted on the struts 7. Thus the struts 7behave substantially as beams in pure compression, i.e. all forcesacting on the struts other than the compressive force are negligible.The struts 7 are therefore not subjected to any forces such as secondaryspring moments that can cause failure in the prior art couplings asdescribed above. The present couplings also have the advantage that theyonly remain stressed so long as an axial load is applied to them. Whensuch a load is removed, the struts 7 will relax. As a result of thisproperty the couplings are very effective at bearing cyclic loads asthey will not be subject to cumulative stressing, exhibited by manyprior art couplings, which can lead to failure.

As described above the relative independence of the struts 7 within thelocking ring is important to the strength of the coupling. The forcesapplied by the spring portions 8 to the struts 7 serve only to maintainthe struts 7 in the required array when there is no load on the couplingand to provide the necessary biasing force to ensure the edges 9 and 10bear against the socket 11 and spigot 13 respectively. The spring forcesplay no part in resisting axial loads.

The force exerted by the spring portions 8 can be minimised byincreasing the depth of the slots 5 and 6 in each pair and cutting themcloser together. FIG. 4 shows a locking device in which the spring forcehas been further reduced by cutting further circular slots 14 radiallythrough the ring at the location of the slots 5 and 6. The slots 14divide the spring portions 8 into two much smaller spring portions witha resultant decrease in the spring force applied to the struts 7.

There are many different possible applications and modifications of thesimple coupling described above. An example of a coupling to be used tojoin two lengths of pipe is illustrated in FIG. 5. The illustratedcoupling has a substantially cylindrical body 15 with an internalannular flange 16 which defines sockets 17 and an internal tubularchannel dimensioned to receive pipes 18. The flange 16 is itselfprovided with a radially inward extending annular flange 19 intermediateits ends. Locking rings are inserted into the sockets 16 in the mannerdescribed above such that the struts 7 assume the positions shown. Thepipes 18 are then inserted into the coupling through the sockets 17 andthe locking rings until they abut the flange 17. The locking rings aredimensioned to engage the facing cylindrical surfaces defined by theouter wall of the pipes 18 and the inner wall of the sockets 17. Theflange 16 is provided with "O" rings 20 to seal the pipes 18 within thecoupling. The locking rings functions as described above in relation toFIG. 3.

The couplings so far described are of a type that cannot be releasedonce formed. This is because once the struts 7 have bitten in to boththe spigot and socket the locking ring cannot be withdrawn from thecoupling. Examples of releasable couplings according to the presentinvention are illustrated in FIGS. 6 to 8. Each of FIGS. 6 to 8 showsone half of a coupling of the type described above and illustrated inFIG. 5 but with modifications to allow the coupling to be released onceformed. In each case the radially outer edges of the struts 7 arerounded off so that they will not bite into the internal wall of thesocket 17. The couplings are instead provided with restraining meansthat prevent the rounded radially outer edges of the struts 7 fromsliding along the internal wall of the socket and therefore enable themto form a hinge with the socket wall.

The coupling of FIG. 6 is provided with a removable annular flange 21which is fixed on to the end of the fitting around the mouth of thesocket 17 by means of bolts 22. The flange 21 restrains the axialmovement of the struts 7 along the inner surface of the socket 17 whenload is applied to the coupling. The rounded edges 9 of the struts 7form hinges in the corner formed between the flange 21 and the internalsurface of the socket 17 whilst the edges 10 of the struts 7 form hingesby biting into the pipe wall. In all respects other than the means bywhich the outer hinge is formed the modified struts 7 function asdescribed above. To release the coupling the removable flange 21 issimply unbolted from around the mouth of the socket 17 so that the ringcan be withdrawn from the coupling.

Alternative means for retaining the locking ring 1 within the socket 17are shown in FIGS. 7 and 8. The restraining means illustrated in FIG. 7comprises a cir-clip 23 which is located in an annular groove providedon the internal wall of the socket 17. The restraining means shown inFIG. 8 comprises an insert member 24 which is located within the socket17 by means of bayonets 25 which cooperate with suitable formations (notshown) on the internal wall of the socket 17. The bayonet fitting allowsfor easy insertion and removal of the insert member 24.

The locking device retaining means, 21, 23 and 24, do not have to beparticularly securely fastened to the socket 17 as virtually all of theforce on the hinge formed by the rounded edge 9 of the struts 7 is bornby the internal wall of the socket 17. The axial force acting on therestraining means is negligible, the retaining means serving simply toenable the hinge to be established and subsequently released.

The couplings so far described are not very suited to the joining ofsoft materials which are not hard enough to bear the compressive forcein the struts 7. For example if the above described fittings were usedin conjunction with a composite tube which is very strong and light buthas a soft matrix, then the hinge forming edges 10 of the struts 7 woulddig deeply into the tube allowing the struts 7 to pivot fully andreverse their orientation within the annular gap between the tube andthe socket so that the tube can be withdrawn from the socket. However,the present couplings can be used to join soft materials if the spigotis first fitted with a spreader plate, an example of which isillustrated in FIG. 9.

The illustrated spreader plate is formed from a tube 26 of a strongmaterial and provided with circumferentially spaced pairs oflongitudinal slots 27 in an arrangement similar to that of the slots 5and 6 cut into the locking ring. The result is a relatively flexibletubular structure that can be fixed around a soft spigot before such aspigot is inserted into the socket of the coupling. The edge 10 of thestruts 7 can then form a hinge on the relatively hard spreader platewhich will bear a much greater load than a hinge formed on the softermaterial of the spigot.

Examples of couplings incorporating such a spreader plate areillustrated in FIGS. 10 and 11. FIG. 10 illustrates the use of aspreader plate 26 in a pipe coupling for coupling a relatively soft pipe28 to a fitting. FIG. 11 shows the use of a spreader plate 26 in acoupling to be used to secure a rope 29 or the like to a fitting.

FIGS. 12 and 13 illustrate the use of the above described locking ringsin a coupling adapted to be used as a fixing, for example to fix afitting to a wall or other such surface. In the fixing shown in FIG. 12three such locking rings are assembled on to a pin 30 and located withinannular grooves which assist the edges 10 of the struts 7 inestablishing a hinge on the pin 30. One end of the pin 30 is threaded toreceive a nut 31. A hole 32 of appropriate dimensions is drilled into asurface 33 to provide the necessary socket for the coupling. The pin 30,with locking rings already fitted, is then pushed into the hole 32 suchthat the threaded end extends from the hole 32. The rings will functionas described above to prevent the pin 30 from being withdrawn from thehole 32. A fitting 34 can then be fitted over the threaded end of thepin 30 and secured thereto by the nut 31. A plurality of locking ringsare provided in this form of coupling to ensure that the load is evenlydistributed and prevent the pin 30 twisting within the hole 32.

FIG. 13 shows the coupling of FIG. 12 in conjunction with a spreaderplate 26, which may be necessary if the internal surface of the walletc. is not sufficiently hard.

FIG. 14 shows an embodiment of the present invention as an electricalconnector. The example shown is that of a copper wire 35 coupled to apin 36 of a plug. The coupling functions in exactly the same way asdescribed above but on a much smaller scale.

As mentioned above an important aspect of the operation of the describedcouplings is the action of the annular arrangement of struts which areessentially independent of each other and therefore behave as beams insubstantially pure compression. The struts need not necessarily bearranged perfectly symmetrically within the coupling but anything otherthan a symmetric annular arrangement will result in an uneven radialforce being applied to the spigot and socket of the coupling which isundesirable.

As described above the function of the spring portions between thestruts is simply to maintain the struts in the required orientation andto provide the necessary force to ensure that the edges 9 and 10 of thestruts bear against the surface of the sockets and spigots respectively.However, it will be appreciated that there are many alternative ways inwhich this can be achieved. For instance, the struts could be arrangedin annular array and interconnected by means of a rubber collar. Theannular rings previously described could be provided with many differentnumbers of pairs of slots 5 and 6 defining more or less struts 7.

Referring to FIGS. 15 to 18, the illustrated embodiment of the inventionincorporates a six-sided locking device received in a six-sided socket.The locking device defines a circular central aperture intended toreceive a spigot (not shown) having a cylindrical outer wall.

The locking device comprises six load bearing members 37 to 42 with eachadjacent pair of load bearing members interconnected by a strip ofmaterial defined between two parallel slots. One of each pair of slotsextends radially outwards from the edges 43 to the circular aperture,whereas the other of the pair of slots extends radially inwards from theouter edge 44 of the device which engages the socket 45.

The edges 44 lie on a common plane perpendicular to the length of thesocket 45. In contrast, the edges 43 define portions of a helix. Aspigot (not shown) can be inserted into the socket in the directionindicated in FIG. 17 by arrow 46. This causes the load bearing membersto pivot slightly about hinges defined by the outer edges 44. The spigotcannot then be withdrawn as the edges 43 engage the spigot and the loadbearing members pivot backwards about edges 44, jamming the load bearingmembers in engagement with both the socket and the spigot. The couplingcan however be disengaged by rotating the spigot anti-clockwise relativeto the socket looking in the direction of arrow 46 in FIG. 17. The edges43 define a thread through which the spigot can be screwed until the endemerges from the locking device.

It will be appreciated that in the embodiment of FIGS. 15 to 18 rotationof the spigot relative to the socket must cause the spigot to rotaterelative to the locking device as rotation of the locking devicerelative to the socket is prevented as a result of their makingsix-sided shapes. The socket could however by cylindrical but in such aconfiguration it would be necessary to key the locking device to thesocket to prevent relative sliding movement between them.

Alternatively, if both the socket and spigot define cylindrical surfacesengaged by the locking device, both the radially inner and radiallyouter edges of the locking device would define helices such thatdisengagement of the coupling could be achieved whichever edge wascaused to slide relative to the surface against which it bears.

The embodiments of the invention described above rely on the stiffnessof the tube which is inserted into the coupling to prevent the tube fromcollapsing radially inwards when an axial load is applied. The inventioncan be used with tubes that are not stiff provided the tubular insert ispushed into the tube end before the tube end is inserted into thecoupling. A simple cylindrical insert may be used, but it is preferredto use an insert that has an annular groove formed in its radially outersurface, the annular groove being axially aligned with the lockingdevice. FIG. 19 illustrates such an arrangement.

Referring to FIG. 19, a low stiffness thermoplastics tube 47 receiveswithin its end a tubular insert 48. The insert supports a flange 49 tolimit the depth of insertion of the insert, and a portion 50 of the wallof the insert is deflected radially inwards to define a groove facingradially outwards. The tube 47 and the insert 48 are pushed into thesocket of a coupling body substantially identical to that illustrated inFIG. 5, the coupling body receiving a locking ring 51 in an annulargroove 52 that is axially aligned with the portion 50 of the insert whenthe insert flange 49 abuts the inner end of the socket.

The insert 48 may be made from for example a stiff thermoplasticsmaterial or metal. If the tube 47 is under pressure, the insert will notneed to support much of the radial force applied to the tube. If thetube is subjected to a simple axial load however, the insert 48 must bepresent to support the loop compressive load.

Given the groove in insert portion 50, the tube 47 is supported at itsnormal diameter on either side of the point where the locking ringengages the tube. At the point the locking ring engages the tube, as theload is applied the tube is deformed into the groove defined in theinsert. This considerably increases the pull-out strength of thecoupling.

I claim:
 1. A coupling, comprising a first member defining a socket;asecond member defining a spigot inserted into an open end of the socket;and, a locking device received within an annular gap defined between aninner wall of the socket and an outer wall of the spigot, wherein thelocking device comprises a plurality of circumferentially spacedrelatively stiff load bearing members interconnected by relativelyflexible interconnecting means, each load bearing member extendingwithin the annular gap between a first end which is relatively close tothe open end of the socket and a second end which is relatively remotefrom the open end of the socket, the interconnecting means resilientlybiasing each load bearing member such that the first end engages thesocket and the second end engages the spigot, the interconnecting meansenabling each load bearing member to pivot about the first and secondends substantially independently of the other load bearing members, suchthat each load bearing member acts as a beam in compression to resistwithdrawal of the spigot from the socket, the locking device furthercomprising an annular member of resilient material defining a frontface, a back face, a radially inner surface and a radially outersurface, the annual member being provided with a plurality of radialslots grouped in pairs, the annular member being provided with aperturesextending radially therethrough at the location of each pair of slots,one slot of each pair extending radially outwards from the radiallyinner surface of the annual member and the other extending radiallyinwards from the radially outer surface of the annular member, thearrangement being such that a load bearing member is defined betweenneighboring pairs of slots and each pair of slots defines said flexibleinterconnecting means between adjacent load bearing members.
 2. Acoupling, comprising a first member defining a socket;a second memberdefining a spigot inserted into an open end of the socket; and, alocking device received within an annular gap defined between an innerwall of the socket and an outer wall of the spigot, wherein the lockingdevice comprises a plurality of circumferentially spaced relativelystiff load bearing members interconnected by relatively flexibleinterconnecting means, each load bearing member extending within theannular gap between a first end which is relatively close to the openend of the socket and a second end which is relatively remote from theopen end of the socket, the interconnecting means resiliently biasingeach load bearing member such that the first end engages the socket andthe second end engages the spigot, the interconnecting means enablingeach load bearing member to pivot about the first and second endssubstantially independently of the other load bearing members, such thateach load bearing member acts as a beam in compression to resistwithdrawal of the spigot from the socket, the locking device furthercomprising an annular member of resilient material defining a frontface, a back face, a radially inner surface and a radially outersurface, the annual member being provided with a plurality of radialslots grouped in pairs, one slot of each pair extending radiallyoutwards from the radially inner surface of the annual member and theother extending radially inwards from the radially outer surface of theannular member, the arrangement being such that a load bearing member isdefined between neighboring pairs of slots and each pair of slotsdefines said flexible interconnecting means between adjacent loadbearing members, the load bearing members bearing against a cylindricalsurface and the portions of the load bearing members which bear againstthe cylindrical surface defining sections of a helix such that thecoupling may be disengaged by relative rotation between the spigot andsocket.
 3. A coupling, comprising a first member defining a socket;asecond member defining a spigot inserted into an open end of the socket;and, a locking device received within an annular gap defined between aninner wall of the socket and an outer wall of the spigot, wherein thelocking device comprises a plurality of circumferentially spacedrelatively stiff load bearing members interconnected by relativelyflexible interconnecting means, each load bearing member extendingwithin the annular gap between a first end which is relatively close tothe open end of the socket and a second end which is relatively remotefrom the open end of the socket, the interconnecting means resilientlybiasing each load bearing member such that the first end engages thesocket and the second end engages the spigot, the interconnecting meansenabling each load bearing member to pivot about the first and secondends substantially independently of the other load bearing members, suchthat each load bearing member acts as a beam in compression to resistwithdrawal of the spigot from the socket, the locking device furthercomprising an annular member of resilient material defining a frontface, a back face, a radially inner surface and a radially outersurface, the annual member being provided with a plurality of radialslots grouped in pairs, one slot of each pair extending radiallyoutwards from the radially inner surface of the annual member and theother extending radially inwards from the radially outer surface of theannular member, the arrangement being such that a load bearing member isdefined between neighboring pairs of slots and each pair of slotsdefines said flexible interconnecting means between adjacent loadbearing members, the load bearing members bearing against a cylindricalsurface and the portions of the load bearing members which bear againstthe cylindrical surface defining sections of a helix, wherein both theradially inner and outer ends of the load bearing members definehelices, each engaging a respective cylindrical surface in the coupling,such that the coupling may be disengaged by relative rotation betweenthe spigot and socket.
 4. A coupling, comprising a first member defininga socket;a second member defining a spigot inserted into an open end ofthe socket; and, a locking device received within an annular gap definedbetween an inner wall of the socket and an outer wall of the spigot,wherein the locking device comprises a plurality of circumferentiallyspaced relatively stiff load bearing members interconnected byrelatively flexible interconnecting means, each load bearing memberextending within the annular gap between a first end which is relativelyclose to the open end of the socket and a second end which is relativelyremote from the open end of the socket, the interconnecting meansresiliently biasing each load bearing member such that the first endengages the socket and the second end engages the spigot, theinterconnecting means enabling each load bearing member to pivot aboutthe first and second ends substantially independently of the other loadbearing members, such that each load bearing member acts as a beam incompression to resist withdrawal of the spigot from the socket, thelocking device further comprising an annular member of resilientmaterial defining a front face, a back face, a radially inner surfaceand a radially outer surface, the annual member being provided with aplurality of radial slots grouped in pairs, one slot of each pairextending radially outwards from the radially inner surface of theannual member and the other extending radially inwards from the radiallyouter surface of the annular member, the arrangement being such that aload bearing member is defined between neighboring pairs of slots andeach pair of slots defines said flexible interconnecting means betweenadjacent load bearing members, the load bearing members bearing againsta cylindrical surface and the portions of the load bearing members whichbear against the cylindrical surface defining sections of a helix, theradially inner edges of the load bearing members defining a helix freeto slide relative to the cylindrical surface against which they bear,the radially outer edges of the load bearing members being preventedfrom sliding relative to the surface against which they bear, such thatthe coupling may be disengaged by relative rotation between the spigotand socket.